U.S. Pat. No. 4,742,346 issued to Gillette (included herein by reference) illustrates a liquid crystal display (LCD) device incorporating signal drive circuitry integrated together with the LCD elements on a common substrate. Included in the drive circuitry are a plurality of programmable counter circuits. Binary values representative of image brightness are applied to these counters which generate pulses having durations proportional to the binary values. The pulse durations are subsequently converted to potential amplitudes for application to individual display elements.
Consider that the pulses are to represent eight bit binary values, and the longest pulse is approximately equal to the active portion of one horizontal line of video signal, that is approximately 50 .mu.sec. To satisfy these constraints the counter must count at a rate of approximately 5 MHz, e.g., the reciprocal of 50/256 .mu.sec. Now if the counter circuitry is to be realized using amorphous silicon (aSi) transistors as is desirable for economic reasons, this counting rate tends to be too high to be supported by such circuitry. Secondly, programmable counters tend to be relatively complicated, requiring significant numbers of active devices.